Ecological and taxonomic differences between native and introduced plants of southwestern Ontario

We compared taxonomic and ecological attributes of native and introduced pl anes (N = 1330 and 484 species. respectively) of southwestern Ontario, usin g two regional floras (Essex County and Hamilton-Wentworth Regional Municip ality) for distributions, and published sources for ecological attributes. Most exotics (86.4%) originate from Europe and Asia. Exotic species tended to occur in families having just one-to-few species locally. Seven families (Amaranthaceae, Asteraceae, Boraginaceae, Brassicaceae, Caryophyllaceae, F abaceae, and Malvaceae) were significantly over-represented by exotics comp ared to the distribution of native species in these families, while exotics were significantly under-represented in six families (Cyperaceae, Fagaceae , Juncaceae, Orchidaceae, Potamogotonaceae, and Ranunculaceae). In habitat comparisons, exotic species were significantly over-represented (compared t o native species) in disturbed and degraded habitats and moist substrates, while being under-represented in woodland, thicket, and wetland. Introduced species of southwestern Ontario have life history traits that facilitate s uccess in degraded, disturbed and highly fragmented environments. For examp le, exotics were significantly over-represented by the following life-histo ry traits: short life span, flowering season of four or more months, hermap hrodite sex habit, and very small fruits (< 5 mm). They were significantly under-represented by the monoecious and dioecious sex habits, a flowering p eriod of two months and less, animal-based seed dispersal. and relatively s mall fruits (5.1 - 10 mm). A separate analysis of exotic species found only in undisturbed communities, showed these species to be more likely to occu r in open and moist habitats, to have a tree habit, and an extended floweri ng period, and to produce many seeds per fruit (> 7).